Chameleon?

Scientists tell us that birds are the descendents of the dinasours which were reptiles. Here are a couple of photos from last week of what I believe are the same tom. In the first his throat and caruncles are bright red but in the second they have faded to the blue/white of the rest of his head. I hadn't noticed this before but another photographer I met up with there brought it to my attention and said he had a series of a bird taken over the course of 5-10 seconds which show the transformation. I'm assuming they are able to do this trick by regulating the blood flow into that area. I haven't a clue as to why they might do this. The birds we were looking at didn't appear stressed and were acting quite normally. I'm going back tomorrow and you can bet I'll be looking carefully at this reptilian type phenomena. I'm not including any techs with these as all I did was a crop on each photo to show the bird better. The smaller is the tom as seen first while the larger (actually the same size) shows it minutes later. I thought others might find this of interest and I'm curious if anyone else had seen this happen.